Hi 5150,
I was talking to IP on the telephone uncountable times. It occurs that they don't have an influence on who and when people are invited. In all, the only thing IP seems to do for Cargolux is a "pre-screening" in form of a filtering of applications. They forward the ones who meet the requirement. Cargolux then decides about the rest.
To give you an idea, it took me 8 months to get invited for the first step. Then another 3 months for the final interview. Might take even longer these days, where hirings are postponed
good luck!